Occurence of a value in many lists

i have a Series Object in pandas with 2 columns, one for the indices and one with lists, I need to find if a value occurs in only one of these lists and return it with the most optimal way.

As an example let’s say we have this

i need to return 77 because it occurs in only one of these lists.

Answer

You can use explode then value_counts:

df['list_col'].explode().value_counts().loc[lambda x: x==1]